With an increase in the density and capacity of large-scale integrated circuits (LSIs) in recent years, semiconductor devices are required to have an even thinner circuit line width. A lithographic technique is used to form a desired pattern on a semiconductor device. In the lithographic technique, pattern transfer which uses an original pattern called a mask (or reticle) is performed. The manufacturing of a high-precision mask used for this pattern transfer uses a charged particle beam writing apparatus with excellent resolution.
This charged particle beam writing apparatus typically uses apertures (shaping apertures) to shape a charged particle beam. To be more specific, a circuit pattern to be transferred onto a wafer is decomposed into multiple basic figures, and multiple apertures are used to shape a charged particle beam into the same shape and size as each basic figure. Then, the charged particle beam thus shaped is applied to a resist to write a pattern.
A variable shaped beam (VSB) method is one of the methods for shaping the charged particle beam. In this method, rectangular, triangular, and trapezoid patterns are inputted as the basic figures, and a charged particle beam is shaped into desired size and shape, such as a rectangle or a triangle, by control of the overlap amount of two apertures having opening portions through which the charged particle beam passes.
Such a charged particle beam writing apparatus has a contamination problem caused by carbon and the like existing in the atmosphere. The atmosphere inside the charged particle beam writing apparatus is sometimes contaminated by a component which is not supposed to exist there under normal circumstances. For this reason, when the charged particle beam writing apparatus is operated for a long time, contaminants originating from the component described above might be attached to the opening portion of each aperture (to change the shape of the opening) and consequently change the shape or size of the charged particle beam. This change in the shape or size of the charged particle beam results in a decrease in writing precision.
To overcome this contamination problem, the following charged particle beam writing apparatus has been proposed. Specifically, attachment of contaminants to the surface of the aperture is measured by a film thickness measurement device or an elemental analyzer. Then, when contaminants in a predetermined amount or more are attached, the contaminants are removed through heating with a heater or etching with oxygen plasma or ion beams.
In other words, this charged particle beam writing apparatus configured to measure the attachment of contaminants to the surface of the aperture permits attachment of contaminants up to the predetermined amount. However, even a small amount of contaminants attached to the opening portion of the aperture during writing changes the shape or size of the charged particle beam and thus decreases the writing precision.
Moreover, since the temperature of the aperture needs to be brought to a high temperature of several hundred degrees (e.g., 200° C.) to prevent the contamination, a large amount of current is passed to the heater during writing. If the charged particle beam is deflected due to an influence of a magnetic field produced by the heater in that state, the writing position is shifted, which lowers the writing precision. For this reason, the influence of the magnetic field thus produced needs to be diminished by reducing the current passed to the heater during writing. However, reducing the current in turn decreases the amount of heat produced by the heater, and this makes it difficult to bring the temperature of the aperture to the high temperature of several hundred degrees.
In addition, if the heater (heating wire) is provided directly on the surface of the aperture to bring the temperature of the aperture to the high temperature of several hundred degrees, current flows through the aperture as well. Then, if the charged particle beam is deflected due to an influence of a magnetic field produced by the aperture, the writing position is shifted, which lowers the writing precision, as similar to the above case.